# thevenin equivalent

#### evo21

Joined Nov 17, 2007
5
well im kinda stuck with thevenins equivalent.

i calculated the thevenin voltage source wich gave me 0.1mV (100uV in Pspice), but i dont know how to figure out the equivalent resistance.
after that i dont know how to adapt the thevenin equivalent to the original circuit. can anyone explain me step by step how to do this?

any help is apreciated =)

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Joined May 1, 2007
19
hey evo

i'm just learning this stuff myself so i have an ulterior motive in posting an answer: getting the material straight in my own head. nobody's forcing you to read it. that being said, let's begin.

thevenin's theorem deals with what are called two-terminal networks: these are circuits having two distinguished junctions (breadboard rails) called TERMINALS. in your circuit the terminals are the junctions labelled "a" and "b". a THEVENIN NETWORK is a two-terminal network consisting of a voltage source in series with a resistor, with the terminals hanging off the ends (if you see what i mean). if N is a two-terminal network and L ("load") is a resistor let the ATTACHMENT of L to N be the result of soldering one lead of L to each of the terminals of N. let F be the function that takes a two-terminal network N to the function g such that each g(L) is the current through L in the attachment of L to N. a pair of two-terminal networks are EQUIVALENT iff F(N1)=f(N2). in these terms the claim of the theorem is that any two-terminal network is equivalent to a thevenin network.

hopefully someone will correct that if anything is wrong with it.

now let N be the given two-terminal network and let T be the equivalent thevenin network. let V be the strength of T's voltage source and let R be the resistance of T's resistor. if C is the attachment to T of a load with zero resistance (ie: the result of soldering one end of a wire to each of T's terminals) then clearly the current in C is V/R. since current in T itself is zero, the voltage drop between the terminals of T is V. and since T is equivalent to N, V/R is also the current through the wire in the attachment to N of a load with zero resistance, and V is also the voltage drop between the terminals of N.

again: with a grain of salt. hope it helps.

peace
stm

ps: how did you make the jpeg?

#### recca02

Joined Apr 2, 2007
1,212